We analyze the 'optimal' size of non-deliberating majoritarian committees with no conflict of interest among its members when committees can be persuaded by a biased and informed expert. We find that when this bias is small, the optimal size is one; when it is intermediate, the optimal size increases monotonically in the precision of members' private information; when it is large this relation is non-monotonic. However the optimal committee-size never exceeds five. We also show that biased persuasion typically hurts a larger committee more severely. These results provide important implications on issues like universal enfranchisement, role of expert commentary in a democracy or size of governing boards in firms.